This invention relates to flow-through devices for connection into a fluid flow system. In particular it relates to instrument isolator type devices in which an instrument for measurement of some characteristic of the process fluid, such as pressure or temperature, or to react to a change in some characteristic such as a switch is to be responsively connected to the process fluid, but physically isolated from the process fluid.
Isolation devices are commonly installed in piping systems wherein the process fluid is injurious to or is detrimental to proper operation of instrumentation used to measure certain properties of the flowing fluid. The isolation device physically separates the instrument from the process fluid, while permitting accurate measurement of the specific process variable via the attached instrument. In the flow-through type isolator the sensing member is usually an elastomer member forming a conduit coincident with the pipe cross-section where the variable is to be measured. In these elastomer flow-through isolation devices, the sensing member, usually sleeve or spool shaped, is manufactured separately and is mechanically attached to the isolator body by use of metal or plastic flange rings. The combined geometry of the body and the sensing member creates an annular space between the body and the sensing member in which is placed a sensing fluid to hydraulically link the sensing member to the instrument.
It is consistently a problem addressed by the various designs to obtain a space between the sensing member and the instrument in a construction which is low cost and easy to manufacture, reliable, properly sensitive to the process fluid variables and which will be fully sealed against leakage of both the process fluid and the sensing fluid. The present invention provides new and advantageous means and methods for achieving these goals.